The invention relates to stem cells.
Stem cell populations have been identified in many tissues and are thought to constitute a source of tissue renewal in quiescent, regenerative and pathological conditions. Tumor stem cells are the cell renewal source of a neoplasm and also serve as the seeds of metastatic spread of cancer. While rapidly proliferating tissues such as bone marrow, gut, and epidermis are known to be organized into stem cells and lineages of maturing descendants, the evidence for parallel phenomena in other tissues has been debatable.
Stem cell markers are useful to diagnose cancers and to treat pathological conditions characterized by abnormal or insufficient function of differentiated cells of a mature organ. However, stem cells have been difficult to identify and isolate.
The invention features an antibody that selectively binds to an ectodermally-derived stem cell. Preferably, the antibody that selectively binds to an ectodermally-derived stem cell does not also bind to an endodermally-derived stem cell. More preferably, the antibody that selectively binds to an ectodermally-derived stem cell does not also bind to either an endodermally-derived stem cell or a mesodermally-derived stem cell. Such antibodies include MAb 13.2.7 or 1.33.2. For example, the antibody selectively binds to an epithelial stem cell, a skin stem cell, a neural stem cell, or an occular stem cell. Antibodies that selectively bind to an ectodermally-derived stem cell include MAb 7.22.3, 7.18.1, 7.18.9, 9.5.5, 9.29.1, 7.40.1, 6.39.2, 12.3.2, 6.9.2, 6.19.10, 13.2.7 or 1.33.2. The invention also includes an antibody which binds to an epitope identified by MAb 7.22.3, 7.18.1, 7.18.9, 9.5.5, 9.29.1, 7.40.1, 6.39.2, 12.3.2, 6.9.2, 6.19.10, 13.2.7 and 1.33.2. A method of isolating an ectodermally-derived stem cell from a heterogenous population of cells is carried out by contacting a heterogenous population of cells with one or more of the antibodies described above.
The invention also includes an antibody that selectively binds to an endodermally-derived stem cell. Preferably, the antibody does not bind to a bile duct stem cell or a liver stem cell. The antibody that selectively binds to an endodermally-derived stem cell does not bind to an ectodermally-derived stem cell and/or does not bind to a mesodermally-derived stem cell.
One example of an endodermally-derived stem cell-specific antibody is one that selectively binds to a prostate stem cell. In another example, the antibody selectively binds to a prostate stem cell and also selectively binds to a liver stem cell. Preferably, the antibody that selectively binds to a prostate stem cell and further selectively binds to a liver stem cell does not bind to a skin stem cell. For example, MAb 6.39.2 binds to a prostate and liver stem cell but not a skin stem cell.
The antibodies described herein are useful to identify and isolate tissue-specific stem cells. For example, a method of isolating an endodermally-derived stem cell from a heterogenous population of cells includes the step of the contacting population with an antibody that selectively binds to an endodermally-derived stem cell.
Yet another aspect of the invention is a method of diagnosing a neoplasm in a subject, by contacting a tissue sample from a subject such as a human patient with an antibody that selectively binds to an ectodermally-derived stem cells or one that selectively binds to an endodermally-derived stem cell.
Stem cells are also isolated by removing non-stem cells, i.e., differentiated or mature cells, from a heterogeneous population. Such a negative selection approach carried out alone or in combination with the positive selection method described above is useful to isolate stem cells.
The invention encompasses an antibody selected from the group consisting of MAb 3.40.7, 5.37.1, 5.37.4, 8.36.1, 12.3.3, and 14.33.7. Such antibodies bind to cells which are not stem cells. A negative selection method of isolating a stem cell from a heterogenous population of cells involves contacting a heterogeneous population of cells with an antibody selected from the group consisting of MAb 3.40.7, 5.37.1, 5.37.4, 8.36.1, 12.3.3, and 14.33.7 under conditions to form an antibody-cell complex, and removing the complex from the population. Removal of non-stem cells (i.e., non-stem cell-Ab complexes) from the heterogeneous population of cells leaves a population of isolated stem cells. By a isolated population of isolated stem cells is meant a population of cells in which at least 70%, preferably 80%, preferably 85%, preferably 90%, more preferably 95%, more preferably 99% of the cells are stem cells. For example, the population is 100% stem cells. The percentage of stem cells in a population of cells is determined by known methods such as fluoresence-activated cell sorting.
The invention encompasses not only an intact monoclonal antibody, but also an immunologically-active antibody fragment, e.g., a Fab or (Fab)2 fragment; an engineered Fv molecule; or a chimeric molecule, eg., an antibody which contains the binding specificity of one antibody, e.g., of murine origin, and the remaining portions of another antibody, e.g, of human origin. Preferably, the antibody has a binding affinity of at least about 108 liters/mole and more preferably at least about 109 liters/mole. Humanized monoclonal antibodies are also within the invention. Monoclonal antibodies of non-human origin, e.g., mouse monoclonal antibodies, are humanized by methods known in the art. For example, mouse monoclonal antibodies with a desired binding specificity are commercially humanized (Scotgene, Scotland or Oxford Molecular, Palo Alto, Calif.).
By xe2x80x9cselectively bindsxe2x80x9d is meant that the antibody binds to stem cells with at least 50% greater affinity than the affinity with which it binds to a known differentiated or mature cell, preferably at least 60%, preferably at least 70%, preferably at least 80%, preferably at least 85%, preferably at least 90%, more preferably at least 95%, more preferably at least 99% greater. The binding affinity of an antibody can be determined by methods known in the art.
All technical and scientific terms used herein have the same meanings commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice of the present invention, the preferred methods and materials are now described. The citation or identification of any reference within this application shall not be construed as an admission that such reference is available as prior art to the present invention. All publications mentioned herein are incorporated herein in their entirety by reference.